The fit of a prosthesis determines the function of the user to a great degree. In the extreme, a painful fit will result in non-use of the prosthesis. Diurnal, menstrual and other fluctuations in body weight lead to noticeable changes in comfort and function of a prosthesis. As a consequence, the relative quality of socket fit determined by socket volume is of paramount concern in the daily lives of persons with limb loss The objective of the proposed work is to build on the demonstrably successful Phase I effort to develop an Equilibrium Socket System (ESS) for Lower Limb Prostheses. The Phase I work undertaken by the Orthocare Innovations team has resulted in identification successful demonstration of an approach that can be developed into a clinically relevant, commercially viable system for dynamically adjusting prosthesis sockets. While both socket volume, and vacuum suspension systems have been developed previously, the approaches taken often work against each other and sometimes against normal physiological change. The unique feature of the ESS is that combines both autonomous and user adjustable level of dynamic volume accommodation using a simple mechanism, coupled with a silent, dynamically adjusting vacuum suspension system. The system will allow both the prosthetist and the patient to control socket volume changes and suspension in a way that accommodates normal volume fluctuation. The technology will enable the patient to participate more fully by directly controlling adjustments based on what they feel. In the proposed work, we will design and build the definitive system from the lessons learned in Phase I, evaluate performance and feasibility with human subjects, review the results with the subjects and colleagues in clinical prosthetics, and transition the final design to manufacture. PUBLIC HEALTH RELEVANCE: This project will improve the fit and function of prostheses by creating a dynamically and automatically adjusting socket interface with the amputated limb. The technology will allow the prosthesis user to adjust the firmness of the fit of their prosthesis quickly, easily, and in a more precisely controlled manner than is currently possible.